Water purification devices which purify at slow rate, such as those which use the distillation and the reverse-osmosis processes, deliver water into a storage tank or reservoir from which the water is dispensed. The same is true in regard to systems which use bottled water and water filter dispensing coolers. The water, however, may be easily contaminated with bacteria by contact with air on the storage and dispensing mechanisms, or merely by sitting stagnant in the reservoir. This is particularly true with bottled water cooler dispensers and those units that are used as replacements for bottled water cooler dispensers since the tanks are non-pressurized, and therefore must be vented to permit water to be dispensed by gravity flow.
A known method for eliminating bacterial contamination is the use of ultra-violet ("UV") light. The light energy from a UV lamp is germicidal, because UV light penetrates microbial organism's protective membrane layer and photochemically damages the DNA structure, disabling its self-reproducing capability and rendering the cell lifeless.
UV light is in the region of the electromagnetic spectrum that lies between visible light and X-rays. The ultra-violet spectrum ranges from 100 nm to 400 nm wave lengths, with the optimum effective range between 250 nm to 270 nm. The UV lamp is commonly housed in a protective sleeve of quartz which is similar to a test tube that allows ultra-violet transmission and separates the lamp and wiring from the water surrounding the lamp. The quartz sleeve also helps the UV lamp to maintain its optimal operating temperature of approximately 105.degree. F. Factors that determine a UV system's effectiveness include the intensity of the lamp, the exposure time of the water to the ultra-violet rays and the water transmission rate which is determined by the quality and color of the water.
The typical storage reservoir for water purification units is not suitable for effective UV application. In gravity-filled storage reservoirs, there must be a method for controlling the water level within the reservoir, and typically a float valve or switch is used. With a UV bulb inside the reservoir, a float valve or switch will normally act as an obstruction to the UV light rays, and provide a sheltered location for bacterial contamination to grow. A typical size and storage capacity for a point of use reservoir is in the order of approximately 4 to 6 gallons, which is required to compensate for the slow recovery rate of the purification system. Since UV has a limited effective transmission distance, the physical dimensions of a 4 to 6 gallon storage reservoir have not been suitable for effective UV application. A very high intensity UV lamp would be required in such cases and this would heat the chilled water thereby reducing the efficiency and effectiveness of the chilling process. Moreover, UV degrades most plastics, and typically in large reservoirs, floats and switches are constructed of plastic. A typical point of use and bottled water dispenser reservoir is divided into two compartments by an internal baffle that separates the water which has been cooled from the water that is still at room temperature. Two faucets are used, one for dispensing room temperature water and the other for dispensing chilled water. The baffle that separates the cold and room temperature sections blocks UV rays from reaching one of the compartments in such systems.
It was pointed out in the aforesaid copending patent application that the known prior art has not solved any of these problems. In Marsh U.S. Pat. No. 5,441,179, an apparatus is shown for disinfecting water in a water cooler holding tank using a UV lamp in the form of a collar incorporated within the bottle positioning collar on top of the base where the neck of the bottle is inverted to dispense water into the holding tank. The problem with a system of this type is that substantially all of the bottled water dispensers on the market today are designed to dispense water at both room temperature and at a chilled temperature. To separate the different temperature compartments an internal baffle is used to form a barrier between upper and lower portions of the holding tank, the lower portion being cooled externally by a cooling means such as a compressor system or thermal-electric cooling system. Water is drawn from above the baffle to dispense room temperature water, and water is drawn from the base of the holding tank to dispense chilled water, taking advantage of the natural temperature inversion. The UV lamp located above the water line in the holding tank has substantially no beneficial sterilization effects on water located below the baffle. A major cause of bacterial contamination of water in holding tanks is a build up of bacterial "slime coat" on the tank walls, which provide a breeding ground and contact point for water to be dispensed. Any water dispensed from below the baffle in this arrangement would pass through a non-treated area of the tank and become contaminated. Moreover, a UV lamp placed above the water line has only one side of the UV lamp exposed toward the water to be treated and is not as effective as an immersed UV lamp that exposes the water to the full 360 degrees of the lamp output. Placing a lamp in the center of a storage tank also lowers the required UV light transmission distance by half. Furthermore, since UV light degrades most plastics and since most bottles are constructed from plastic, exposing the neck of the water bottle either directly or indirectly to UV light will have an adverse effect on the bottle material over time. Additionally, harmful UV light may be transmitted to the eyes of a person while a plastic bottle is being changed.
In Kohlman and Karmain U.S. Pat. Nos. 5,316,673 and 4,276,256 respectively, a UV lamp is located within dispensing apparatus to sterilize water as it is being dispensed. Bacterial growth that occurs inside the storage tank, and the build up of bacterial "slime coat," which can be the cause of bad tasting and smelling water, however, will not be remedied by treatment with UV light as the water is being dispensed. In Valadez U.S. Pat. No. 4,969,991, a subsystem for circulating water from a reservoir through a microbial sterilizer (such as UV) periodically utilizes a pump to recirculate the water out of the holding tank through the UV in-line filter and back to the holding tank. Again, bacterial growth that can occur on the inside of the holding tank surfaces is not affected since UV treated water has no residual anti-bacterial properties.
In Sherman, U.S. Pat. No. 5,389,254, a purification system is disclosed which is coupled to a pressurized holding tank with a UV lamp and a diaphragm, the diaphragm being rubber and located at the base of the holding tank to maintain pressure in the tank and to deliver the water. Again, UV light is destructive to most plastic and to rubber materials. An internal diaphragm would create shaded areas between the diaphragm and the tank walls providing an area for growth of bacteria in the holding tank thereby making the holding tank a source of contamination.
In Ho, U.S. Pat. No. 4,322,291, an apparatus is disclosed having a horizontally placed UV lamp inside a tank with a series of concentric plates, the function of the plates being to effect a uniform water flow across the horizontally placed UV lamp.
In Dung, U.S. Pat. No. 5,675,973, a purifier is disclosed wherein water under pressure is forced through a number of filters, the last one being a UV filter. Woodward, U.S. Pat. No. 5,484,538 is similar.
Hamlin, U.S. Pat. No. 5,112,477, shows vending machine apparatus with water UV being treated just prior to dispensing, while Matsumoto, U.S. Pat. No. 5,321,908, discloses placing germ killing antibacterial material in a holding tank.
Accordingly, the prior known art has not solved the problems heretofore noted. These problems are the result of water sitting stagnant for a time in a reservoir. When water is constantly flowing, there is little, if any, chance for bacterial buildup, but when water is stagnant, contamination may readily occur.
In my aforesaid copending patent application a water dispensing system for dispensing room temperature and chilled water included an ultraviolet purifying tank having a separating baffle separating the tank into a room temperature water compartment and a chilled water compartment, the tank carrying a UV energy source extending into both compartments, the treatment tank having no ultraviolet light blocking obstacles so that substantially all of the rays reach the water. The ultraviolet source preferably is a UV lamp in a quartz sleeve positioned in the center of the treatment tank so that the output of a full 360 degrees of the rays reach the water. Thus, there are two compartments, each holding water at a different temperature, and the UV lamp is mounted such as to be disposed in each compartment. To prevent the ultraviolet light from being blocked by components that may itself be at a location to shelter bacteria growth, such as a float valve or switch, the proposal used an external control providing a simple float level control mounted within a housing separated from the treatment tank. However, although such a system provides satisfactory results in a large dispensing apparatus, in smaller systems such as coolers, the use of an external level control is impracticable. Moreover, it is highly desirable to utilize an ultraviolet lamp having low power requirements. A problem also results when water is flowing through the system under full flow conditions because some of the water may not receive ultraviolet light rays for a sufficient time, and this is significant if the water has not previously been purified. A system using a high wattage lamp, as aforesaid, requires additional power to cool the water which is to be chilled. Thus, there is a two fold effect on the power requirements of the system when a UV lamp having a high power requirement is used.